Watch the time in service on the Vac pump *right around 500 hours time
in service WATCH OUT!

I've never considered replacing the vacuum pump as preventive
maintenance, but looking back at my Mooney experience, that's not a
bad idea. I don't think I've had one last as long as 1000 hours and
two failed in the clouds. It goes to show the instrument failure gods
have a sense of humor: I doubt as much as 20% of the time I fly with
no outside reference, but two of four failures were in those
conditions. Murphy was right: if it's going to go wrong it'll happen
at the worst possible time.

Thanks for a good idea: obvious once stated!